Electron beam processing method and apparatus

ABSTRACT

An organic material film formed on a surface of an object to be processed is cured by electron beams irradiated thereon through a hydrocarbon radical generating gas. By employing the electron beams and the hydrocarbon radical generating gas, a deterioration of a k value of the organic material film and a reduction of a chemical resistance thereof are suppressed.

FIELD OF THE INVENTION

[0001] The present invention relates to an electron beam processingmethod and apparatus for reforming an organic material film such as aninterlayer insulating film by employing electron beams.

BACKGROUND OF THE INVENTION

[0002] With the development of high integration and high speedsemiconductor devices, wiring structure thereof is becoming finer andreduction of electrical capacitance between wirings is getting more andmore important. To meet such technical requirements, an organic materialof a low dielectric constant has been developed as a low-k film materialfor use in forming an interlayer insulating film. Since, however, thelow-k film material dose not have sufficient mechanical strengthrequired as the interlayer insulating film, there have been recentlysuggested various methods for enhancing the mechanical strength of theorganic material film by using electron beams. For example, disclosed inJapanese Patent Laid-open Publication No. 2000-221699 (paragraphs[0015], [0016] and [0020]) is a curing method for improving a filmquality of an organic material film such as a resist film or anantireflection film by facilitating a carbonization reaction by way ofirradiating electron beams thereto in oxidizing or reducing atmosphere.Further, U.S. Pat. No. 6,652,922 discloses another curing method forhardening an organic material by way of irradiating electron beamsthereto in the presence of oxygen (O₂), argon (Ar), nitrogen (N₂),helium (He) or a combination thereof, thereby improving a heatresistance or a plasma resistance of the organic material film of a lowdielectric constant.

[0003] Though such curing methods serve to improve mechanical strengthof the organic material film by hardening a surface region thereofthrough the use of electron beams, there remain certain problems in thatthe k value at the surface region of the organic material film may bedeteriorated or methyl groups may be decomposed, to thereby reduce achemical resistance thereof during a cleaning process, for example.

SUMMARY OF THE INVENTION

[0004] It is, therefore, an object of the present invention to providean electron beam processing method and an apparatus capable ofsuppressing a deterioration of k value of an insulating film and areduction of chemical resistance thereof.

[0005] In accordance with one aspect of the present invention, there isprovided an electron beam processing method for processing an organicmaterial film formed on a surface of an object to be processed by usingan electron beam, wherein the electron beam is irradiated onto theorganic material film through a hydrocarbon radical generating gas.

[0006] In accordance with another aspect of the present invention, thereis provided an electron beam processing apparatus including: ahermetically structured processing chamber; a mounting table disposedinside the processing chamber for mounting thereon an object to beprocessed having an organic material film formed on a surface thereof; aplurality of electron beam tubes disposed above the mounting table; agas supply unit for supplying a hydrocarbon radical generating gas intothe processing chamber; and a depressurization unit for reducing aninner pressure of the processing chamber, wherein the electron beamtubes irradiate electron beams onto the organic material film throughthe hydrocarbon radical generating gas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The above and other objects and features of the present inventionwill become apparent from the following description of preferredembodiments given in conjunction with the accompanying drawings, inwhich:

[0008]FIG. 1 shows an electron beam processing apparatus in accordancewith a preferred embodiment of the present invention;

[0009]FIG. 2 sets forth a plan view of an exemplary arrangement ofelectron beam tubes of the electron beam processing apparatus shown inFIG. 1;

[0010]FIG. 3 depicts a graph of measurement results of a first exampleof the electron beam processing method in accordance with the presentinvention and a first comparative example, which represents arelationship between an irradiation time of electron beams and a kvalue;

[0011]FIG. 4A exhibits a relationship between an irradiation time ofelectron beams and a contact angle for the first example of the electronbeam processing method in accordance with the present invention;

[0012]FIG. 4B provides a relationship between an irradiation time ofelectron beams and a contact angle for the first comparative example;

[0013]FIG. 5A describes a relationship between an irradiation time ofelectron beams and a content ratio of methyl groups for a second exampleof the electron beam processing method in accordance with the presentinvention; and

[0014]FIG. 5B illustrates a relationship between an irradiation time ofelectron beams and a content ratio of methyl groups for a secondcomparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention will now bedescribed with reference to FIGS. 1 to 5B.

[0016] An electron beam processing apparatus 1 of a preferred embodimentof the present invention includes, e.g., as shown in FIG. 1, aprocessing chamber 2 formed of, e.g., aluminum in a manner that adepressurization thereof is possible; a mounting table 3 disposed at acentral portion of a bottom of the processing chamber 2 to mount thereonan object (wafer W) to be processed; and a plurality of (e.g., nineteen)electron beam tubes 4 concentrically arrayed on a ceiling of theprocessing chamber 2 facing the mounting table 3. The processingapparatus 1 irradiates an electron beam onto the entire top surface ofthe wafer W placed on the mounting table 3 from each of the electronbeam tubes 4 under the control of a controller (not shown), therebyreforming a film quality of a coated insulating film (referred to as an“SOD (Spin On Dielectric) film” hereinafter) formed on the surface ofthe wafer W. Such a reforming process using electron beams will bereferred to as an EB (electron beam) cure hereinafter, if necessary.

[0017] Connected to a bottom surface of the mounting table 3 is anelevating mechanism 5. The mounting table 3 is moved upward and downwardvia a ball screw 5A of the elevating mechanism 5. The bottom surface ofthe mounting table 3 and the bottom surface of the processing chamber 2are connected via an expansible and contractible stainless steal bellows6, which allows the inside of the processing chamber 2 to behermetically sealed. Further, provided at a side wall of the processingchamber 2 is a wafer loading/unloading opening 2A. Installed at thewafer loading/unloading opening 2A is a gate value 7 for opening andclosing the wafer loading/unloading opening 2A. Further, the processingchamber 2 is provided with a gas supply port 2B disposed above the waferloading/unloading opening 2A and a gas exhaust port 2C is formed at thebottom surface of the processing chamber 2. Connected to the gas supplyport 2B and the gas exhaust port 2C via a gas supply line 8 and a gasexhaust line 10, respectively, are a gas supply source 9 and a vacuumexhaust system (not shown). Installed on the gas supply line 8 are amass flow controller 11 and a valve 12, through which a source gas issupplied into the processing chamber 2 from the gas supply source 9while its flow rate is being controlled. Reference numeral 13 in FIG. 1represents a bellows cover.

[0018] The mounting table 3 has a heater 3A on a top surface thereof bywhich the wafer w is heated up to a desired temperature. The nineteenelectron beam tubes 4 are arrayed, e.g., as shown in FIG. 2, where oneof the electron beam tubes 4 is disposed at the center of the ceiling ofthe processing chamber 2; six of them are disposed around the one at thecenter and the remaining twelve are placed around the six. Each electronbeam tube 4 has a transparent window installed inside the processingchamber 2 for transmitting an electron beam, and is hermeticallystructured. The transparent windows are made of, e.g., transparentquartz glass. Disposed below the transparent windows in a manner offacing thereto are detectors 4A of a grid pattern. The detectors 4Adetect doses of electrons colliding therewith and then provide detectionsignals to the controller. The controller controls the concentricallydisposed nineteen electron beam tubes 4 based on the detection signalsfrom the detectors 4A.

[0019] Employed as an organic material for forming the SOD film for usein the preferred embodiment is, for example, a low-k material having adielectric constant lower than that (a value of about 4) of quartz. Anorganic material including silicon (Si), carbon (C), hydrogen (H) andoxygen (O) can be used as the low-k material. For example, such anorganic material can be a polyorganosiloxane cross-linkedbenzocyclobutene (BCB) resin, a polyallylene ether (PAE) resin such asFLARE (a trade mark) and SiLK (a trade mark) manufactured by the DowChemical Company, and an organic polysiloxane resin such as methylsilsesquioxane (MSQ). An example of the MSQ-based organic material isLKD manufactured by JSR Corporation. If electron beams are irradiatedonto the SOD film, organic compounds included therein are activated and,as a result, there occurs a cleavage of a chemical binding thereof,thereby generating, e.g., hydrocarbon radicals such as methyl radicals.Such cleavage reaction is continued until a chemical equilibrium isobtained. In the preferred embodiment, a low molecular weighthydrocarbon-based gas, to be described later in detail, is employed inorder to suppress the release of methyl groups from the surface of theSOD film due to the cleavage reaction.

[0020] Any low molecular weight hydrocarbon-based gas can be employed aslong as it can generate hydrocarbon radicals such as methyl or ethylradicals after being converted into a plasma inside the processingchamber 2 by the irradiation of the electron beams, thereby suppressinggeneration of, e.g., hydrocarbon radicals from the organic materialfilm. As such a low molecular weight hydrocarbon-based gas, ahydrocarbon gas having not greater than 3 carbon atoms, e.g., methane,ethane or propane, is preferably employed, and, further, a low molecularweight hydrocarbon gas with a substituent such as halogen can also beused. Furthermore, a silicon compound having alkyl groups such ashexamethyldisilazane (HMDS) can be employed as well. The hydrocarbonradicals generated by the irradiation of the electron beams can serve tosuppress the release of hydrocarbon groups such as methyl groups fromthe surface of the SOD film. Consequently, a reduction of a contactangle on the SOD film is restrained while enhancing a chemicalresistance thereof and suppressing an increase of a k value.

[0021] In the following, there will be described the preferredembodiment of an electron beam processing method using the electron beamprocessing apparatus 1 in accordance with the present invention. Themethod suppresses a decrease in a contact angle on a surface of an SODfilm and a deterioration of a k value by reforming the SOD film formedon, e.g., a wiring film layer on a surface of a wafer W.

[0022] First, the wafer W having the SOD film coated thereon istransferred to the electron beam processing apparatus 1 via an arm of aconveying mechanism (not shown). Then, the gate valve 7 is opened toallow the arm of the conveying mechanism to transfer the wafer W intothe processing chamber 2 through the wafer loading/unloading opening 2Aand then to load the wafer W on the mounting table 3 standing by in theprocessing chamber 2. Subsequently, the arm of the conveying mechanismis withdrawn from the processing chamber 2 and the gate value 7 isclosed to hermetically seal the processing chamber 2. In the meanwhile,the mounting table 3 is elevated by the elevating mechanism 5, so that apredetermined distance is maintained between the wafer W and theelectron beam tubes 4.

[0023] Thereafter, the processing chamber 2 is evacuated by the vacuumexhaust system and, at the same time, a low molecular weighthydrocarbon-based gas (e.g., methane gas) is introduced into theprocessing chamber 2 from the gas supply source 9, so that the airinside the processing chamber 2 is substituted with the methane gas, andthe pressure thereof in the processing chamber 2 is maintained at apredetermined level. At this time, the heater 3A of the mounting table 3starts heating the wafer W to set the temperature thereof at apredetermined level. At this stage, a predetermined voltage is appliedto all of the electron beam tubes 4 to enable electron beams therefromto be irradiated onto the SOD film on the surface of the wafer W.

[0024] While traveling toward the surface of the wafer W, some of theelectron beams serve to convert the methane gas into a plasma andgenerate methyl radicals. Further, the rest of the electron beams thatdirectly arrive at the wafer W give an activation energy to, e.g., MSQforming the SOD film, thereby hardening the SOD film by contracting theMSQ through, e.g., a cross-linking reaction and at the same timepartially cleaving the MSQ at the surface of the SOD film to therebygenerate methyl radicals therefrom. Since, however, methyl radicalsgenerated from the methane gas are already included in the processingchamber 2, the release of the methyl radicals from the surface of theSOD film can be suppressed, thereby preventing a reduction in ahydrophobic property of the surface of the SOD film and, also,suppressing a degradation of a chemical resistance such as a resistanceto a cleaning solution. Moreover, the electron beams do not deterioratean apparent k value of the SOD film even when they are directlyirradiated thereon as descried above.

[0025] A partial pressure of the methane gas in the processing chamber 2is preferably set to be equal to or higher than, e.g., 0.01 Torr and,more preferably, from about 0.1 to 1 Torr. If the partial pressure ofthe methane gas is below 0.01 Torr, it becomes easier for the electronbeams to transmit the methane gas. That is, converting the methane gasinto the plasma by the electron beams becomes difficult in such a case,thereby resulting in a deterioration of the k value of the SOD filmlayer. Further, if the partial pressure of the methane gas isexcessively high, it is likely that the electron beams collide with themethane gas, thereby resulting in energy losses thereof. Accordingly,the number of electron beams arriving at the wafer W is reduced, therebyhampering an efficient ED cure of the SOD film. Furthermore, it ispreferable that a heating temperature of the wafer W be maintained at,e.g., about 200 to 400° C. If the temperature of the wafer W isexcessively low, a sufficient EB cure cannot be performed and, as aresult, sufficient film strength cannot be obtained. Moreover, if thetemperature of the wafer W is too high, it is likely that the k value ofthe SOD film is deteriorated.

[0026] In the preferred embodiment as described above, since theelectron beams are irradiated onto the SOD film on the surface of thewafer W in an atmosphere of the methane gas, the methyl radicals aregenerated from the methane gas by the irradiation of the electron beams.The thus generated methyl radicals function to prevent reduction of thechemical resistance of the SOD film by suppressing the release of themethyl groups from the SOD film. Further, by the irradiation of theelectron beams onto the SOD film, the EB cure of the SOD film can becarried out.

[0027] Moreover, since the partial pressure of the methane gas is set tobe not lower than 0.01 Torr in accordance with the preferred embodimentof the present invention, the deterioration of the k value of the SODfilm or the degradation of the chemical resistance thereof can be moreeffectively suppressed. In addition, by using the MSQ as the SOD filmand the methane gas as the hydrocarbon gas, the release of the methylgroups from the SOD film can be more effectively suppressed.

[0028] Next, there will be described specific examples of the preferredembodiment of the present invention with reference to FIGS. 3 to 5B. Inthe examples, electron beam tubes having transparent windows made oftransparent quartz glass in a thickness of 3 μm were employed and adistance between the transparent quartz glass and a wafer was set to be75 mm.

EXAMPLE 1

[0029] In this example, a wafer W on which an MSQ-based SOD film wascoated with a thickness of 5000 angstroms was prepared. Then, the waferW was processed in an atmosphere of the methane gas under the processingcondition as specified below by employing the electron beam processingapparatus 1. Then, by conducting sampling every two minutes, a k valueand a contact angle of the SOD film were measured and a relationshipbetween the processing time and the k value of SOD film and that betweenthe processing time and the contact angle on the surface of the SOD filmwere investigated. FIGS. 3 and 4A show the measurement results thereof.Further, the SOD film was formed of LKD5109 (manufactured by JSRCorporation).

[0030] [Processing Condition]

[0031] Applied voltage: 21 kV

[0032] Applied current: 250 μA

[0033] Flow rate of methane gas: 100 sccm (partial pressure thereof=0.34Torr)

[0034] Flow rate of Ar gas: 2900 sccm

[0035] Pressure of gas: 10 Torr

[0036] Temperature of the wafer: 350° C.

COMPARATIVE EXAMPLE 1

[0037] Herein, a wafer was processed under the same processing conditiondescribed in Example 1, excepting that only an Ar gas was employed inlieu of the methane gas. As in Example 1, a relationship between theprocessing time and the k value of SOD film and that between theprocessing time and the contact angle on the surface of the SOD filmwere investigated. FIGS. 3 and 4B show the measurement results thereof.

[0038] From the results shown in FIG. 3, it was found that k values inExample 1 using the methane gas were lower than those in ComparativeExample 1 using the AR gas if the processing time was longer than about480 seconds, indicating that the degradation of the k values wassuppressed. Furthermore, from the results shown in FIGS. 4A and 4B, adecremental rate of contact angles was found to be smaller in Example 1using the methane gas than in Comparative Example 1 using the AR gas.From the above, it can be seen that, by performing the EB cure on theSOD film in the atmosphere of the methane gas, the release of methylgroups from the surface of the SOD film can be suppressed, so that achemical resistance such as a resistance to a cleaning solution of theSOD film can be prevented from being reduced without deteriorating the kvalue.

EXAMPLE 2

[0039] In this example, changes in content ratio of methyl groups on thesurface of SOD film were observed by varying thicknesses of the SODfilms. Two types of wafers were prepared: one having thereon anMSQ-based SOD film coated in a thickness of 5000 angstroms and the otherhaving an MSQ-based SOD film coated in a thickness of 1000 angstroms.Then, the wafers were processed under the same processing condition asdescribed in Example 1, and amounts of absorption of infrared rays ofS₁—CH₃ and Si—O of the SOD films were measured by fourier transforminfrared (FT-IR) spectroscopy by performing sampling at two minuteintervals. Ratios of S₁—CH₃/Si—O were calculated from the amounts ofabsorption and the ratios were regarded as the content ratios of methylgroups. The results are provided in FIG. 5A.

COMPARATIVE EXAMPLE 2

[0040] Two types of wafers as described in Example 2 were processedunder the same processing condition as in Comparative Example 1. Then,content ratios of methyl groups were calculated as in Example 2, and theresults are provided in FIG. 5B.

[0041] As can be seen from the results in FIGS. 5A and 5B, in case ofthe SOD films having the thickness of 5000 angstroms, the content ratioof methyl groups decreases in a similar manner in Example 2 andComparative Example 2, exhibiting no noticeable effect of the methanegas employed in Example 2. On the other hand, the results of the SODfilms having a ⅕ of thickness, i.e., 1000 angstroms, show that adecremental rate in Example 2 using the methane gas is smaller than thatin Comparative Example 2 using the Ar gas, indicating that methyl groupsin the plasma of the methane gas serve to reduce an amount of methylgroups released from the SOD film. The effect of the methane gas may notbe observed from a thick SOD film because the FT-IR measurement data cannot exactly reflect changes in the content ratio of the methyl groups ina surface region of the SOD film, even in a case there exist suchchanges. That is, since the FT-IR measures an amount of infrared raysabsorbed by the entire thickness of an SOD film, variations of thecontent ratio of methyl groups in the surface region of a thick SOD filmmay not be detected by the FT-IR due to a relatively higher contentratio of methyl groups in the bulk region thereof.

[0042] The present invention is not limited to the preferred embodimentdescribed above but can be modified in various ways. For example, thegas supplied into the processing chamber is not limited to the methanegas but can be any one of low molecular weight hydrocarbon-based gasesas long as hydrocarbon radicals can be generated therefrom. Such lowmolecular weight hydrocarbon-based gas can be, e.g., ethane, propane ora low molecular weight hydrocarbon gas having a substituent such ashalogen. Moreover, a silicon compound having alkyl groups such ashexamethyldisilazane (HMDS) can also be employed instead of the methanegas. Further, though the preferred embodiment has been described for thecase of performing a curing process on a wafer having thereon a coatedinsulating film (SOD film) by using the methane gas, the preferredembodiment can also be applied to a film formed by CVD. In addition, byirradiating electron beams onto an object to be processed through thegas described above, an organic film can be formed on a surface of anobject to be processed.

[0043] While the invention has been shown and described with respect tothe preferred embodiments, it will be understood by those skilled in theart that various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. An electron beam processing method for processingan organic material film formed on a surface of an object to beprocessed by using an electron beam, wherein the electron beam isirradiated onto the organic material film through a hydrocarbon radicalgenerating gas.
 2. The method of claim 1, wherein the hydrocarbonradical generating gas is a low molecular weight hydrocarbon-based gas.3. The method of claim 2, wherein the low molecular weighthydrocarbon-based gas is set to have a partial pressure equal to orgreater than 0.01 Torr.
 4. The method of claim 2, wherein the lowmolecular weight hydrocarbon-based gas is a methane gas.
 5. The methodof claim 1, wherein the organic material film has a low dielectricconstant.
 6. The method of claim 1, wherein the organic material film ismade of an organic silicon compound.
 7. An electron beam processingapparatus comprising: a hermetically structured processing chamber; amounting table disposed inside the processing chamber for mountingthereon an object to be processed having an organic material film formedon a surface thereof; a plurality of electron beam tubes disposed abovethe mounting table; a gas supply unit for supplying a hydrocarbonradical generating gas into the processing chamber; and adepressurization unit for reducing an inner pressure of the processingchamber, wherein the electron beam tubes irradiate electron beams ontothe organic material film through the hydrocarbon radical generatinggas.
 8. The apparatus of claim 7, wherein the hydrocarbon radicalgenerating gas is a low molecular weight hydrocarbon-based gas.
 9. Theapparatus of claim 8, further comprising a member for setting a partialpressure of the low molecular weight hydrocarbon-based gas to be equalto or greater than 0.01 Torr.
 10. The method of claim 8, wherein the lowmolecular weight hydrocarbon-based gas is a methane gas.
 11. The methodof claim 9, wherein the low molecular weight hydrocarbon-based gas is amethane gas.
 12. The apparatus of claim 7, wherein the organic materialfilm has a low dielectric constant.
 13. The apparatus of claim 7,wherein the organic material film is made of an organic siliconcompound.